Ford Motor Co. engineers and designers working on the next generation of the Ford Mustang face a tough challenge of how to update the original pony car for the 21st century.

While the current generation of the Mustang remains a strong performer on the street and the sales results, it’s showing its age.

The new Ford Fusion in the United States will become the Ford Mondeo in Europe with only a few tweaks; the Fiesta and Focus are already global travelers, and even Ford’s SUV lineup will turn international with the new Escape.

There are exceptions, such as the F-series that dominates American roads and the Ranger pickup sold outside the United States, but the Mustang is the only rear-wheel-drive coupe left in Ford’s stable worldwide.

The next generation of Mustang will need to have an international touch to merit the hundreds of millions of dollars Ford will need to spend designing and building it.

Ford spokespeople decline to talk about new products, and no one at the company has officially said the Evos previews what the new Mustang will look like. But the Evos was heralded as the new corporate face for Ford worldwide, with its Aston Martin-derived cues already showing up on other models.

Specifically, it’s about the right size — shorter by 10 inches than the current Mustang, but with a wheelbase shrunk only an inch. And the rear fenders have a hint of the vent and kick-up from the original Mustang, which also came as a fastback body style.

Making the Mustang an international player would require Ford to build a smaller, lighter car that could get better fuel economy without compromising performance. Ford’s already expected to put a four-cylinder Ecoboost turbo engine in the Mustang before any new model arrives in 2014.